Abstract

Recent successes in achieving highly durable clinical responses with antibodies to immune checkpoint receptors such as CTLA4 and PD1 have transformed the outlook for cancer therapy. While these antibody-based therapies show impressive clinical activity, they suffer from the shortcomings including the need to administer by intravenous injection, failure to show response in majority of patients and immune-related adverse events (irAEs) due to the breaking of immune self-tolerance. Sustained target inhibition as a result of a long half-life (>15-20 days) and >70% target occupancy for months may be factors contributing to irAEs observed.

We sought to discover and develop small molecule immune checkpoint antagonists capable of targeting PD-L1 and another immune checkpoint pathway. We reasoned that such therapeutic agents will be amenable for oral dosing, likely show greater response rate due to dual antagonism and allow better management of irAEs due a shorter pharmacokinetic profile.

A focused library of compounds mimicking the interaction of checkpoint proteins was designed and synthesized. Screening and analysis of the resulting library led to the identification of hits capable of functional disruption of the checkpoint protein(s) signaling depending upon the pockets of sequence similarity of interacting proteins. Further optimization resulted in compounds targeting PD-L1/VISTA or PD-L1/TIM-3 with desirable physico-chemical properties and exposure upon oral administration..

The ability of compounds to disrupt specific immune checkpoint pathways was confirmed though functional studies. Identified lead compounds exhibit potent activity when tested in assays to rescue lymphocyte proliferation and effector functions inhibited by respective ligands/proteins. In a panel of functional assays, the selected lead compounds showed selectivity against other immune checkpoint pathways including CTLA4, LAG3 and BTLA. Lead compounds exhibited sustained immune PD in vitro and in vivo suggesting that drug efficacy may extend beyond drug clearance. Lead compounds exhibited significant efficacy in syngeneic pre-clinical tumor models of melanoma, breast carcinoma and colon cancers upon once a day oral dosing. In repeated dose toxicity studies, the most advanced compound, AUPM-170, a dual antagonist of PD-L1 and VISTA, was well tolerated at >100x of the efficacious doses.

The data demonstrating the inhibition of PD-L1 and another immune checkpoint pathway (VISTA or Tim3) resulting in activation of T cells and anti-tumor activities support further development of these orally bioavailable agents. IND-enabling studies with one of the lead compounds, AUPM-170, are underway towards advancing it to the clinic.